Unit 4 - Immune System K-M Flashcards
Adaptive Immunity creates…
antigen-specific responses
- adaptive immune responses are ANTIGEN-SPECIFIC EVENTS in which the body recognizes a particular foreign substance & selectively reacts to it
Adaptive Immunity
Basic Steps of PRIMARY Response/Exposure:
- Naïve T and B LYMPHOCYTES exposed to antigen for first time (first exposure)
- Clonal expansion occurs (mitosis of B-cells and T-cells that have BCRs/TCRs specific for the antigen)
- Differentiate into effector cells and memory cells.
Effector B-cells = Plasma cells.
Effector T-cells = Helper T cells and Cytotoxic T-Cells - Plasma B cells produce antibodies, Memory B cells remain in circulation (humoral immunity).
Naïve T and B lymphocytes
at birth, each clone of lymphocytes is represented by only a few cells, called native lymphocytes
Clonal expansion
b/c the small # of cells in each naive clone isn’t enough to fight off foreign invaders, the 1st exposure to an antigen activates the appro. clone & stimulates it to cells in the clone
- this process (clonal expansion), creates add. cells in the clone
- naive cells continue to be generated throughout an individual’s lifetime
Effector cells
carry out the immediate response & then die within a few days
Memory cells
long-lived & continue reproducing themselves
Effector B-cells =
Plasma cells
Effector T-cells =
Helper T cells and Cytotoxic T-Cells
Plasma B cells
produce antibodies
- to create humoral immunity, the soluble antibodies of the plasma
Memory B cells
remain in circulation (humoral immunity)
- stay alive, waiting for the next exposure to the same antigen
Antibody production is _____ & ______ in magnitude in the primary immune response b/c _______
SLOWER
LOWER
the body has not encountered the antigen before
Adaptive Immunity
Basic Steps of SECONDARY Response/Exposure: (Immune Memory)
is _____ & ______ b/c _______
QUICKER
LARGER
of the memory B cells that remained behind after the 1st exposure
Adaptive Immunity
Basic Steps of SECONDARY Response/Exposure: (Immune Memory)
- Many MEMORY T and B LYMPHOCYTES in circulation are exposed to same antigen that initiated their formation.
- Clonal expansion occurs more quickly (there is a larger population of memory T and B cells for the specific antigen than there was for Naïve T and B cells during the first exposure).
- Increased number of effector T and B cells and memory T and B cells are formed.
- More plasma cells, results in increased antibody production compared to primary response. More cytotoxic cells allows for faster more effective destruction of infected host cells.
- Overall more cells = more response to 2nd exposure
Adaptive Immunity – Cell Mediated Immunity
Effective against virus infected cells and cancerous cells
Adaptive Immunity – Cell Mediated Immunity
Steps for secondary response:
- Pathogen invades tissues
- Phagocytosis by resident macrophage or dendritic cell.
- Antigen presentation to TYPE 1 Helper T-cells (CD4+) by binding of TCR to antigen-MHC-II.
- Activated Type 1 Helper T cells secrete IL-2 (cytokine) which activates Cytotoxic T-Lymphocytes (CD8+)
- Cytotoxic T-Lymphocyte TCRs bind to antigen-MHC-I complexes on infected host cells.
- Cytotoxic T-Lymphocytes release perforin onto infected host cell membrane, creating a pore.
- Cytotoxic T-Lymphocytes release granzymes into infected host cell which will digest the cell.
- Infected host cell undergoes apoptosis (lysis).
Steps for primary response would be similar (to secondary response for CELL MEDIATED IMMUNITY), but would involve…
antigen presentation to Naïve T cells followed by clonal expansion in between step 2 and 3
Adaptive Immunity – Humoral Immunity
Antibody mediated immunity.
Adaptive Immunity – Humoral Immunity
Steps for secondary response:
- Pathogen invades tissues
- Pathogen recognized by TLRs (Toll like-receptors) or opsonized by complement or antibodies.
- Phagocytosis of pathogen by resident macrophage or dendritic cell.
- Antigen presentation to TYPE 2 Helper T-cells (CD4+) by binding of TCR to antigen-MHC-II.
- Activated TYPE 2 Helper T cells secrete IL-4, IL-5, IL-6 (cytokines) which activate B-cells to proliferate (clonal expansion) and Plasma cells to produce antibodies.
- Antibodies facilitate:
a. phagocytosis (e.g. act as opsonins)
b. cell lysis (apoptosis) via activation of classical complement pathway or
activating degranulation of NKCs and/or eosinophils
c. Facilitate production of more antibodies (though action on B cells)
Adaptive Immunity – Humoral Immunity
- Antibodies facilitate:
a. phagocytosis (e.g. act as opsonins)
b. cell lysis (apoptosis) via activation of classical complement pathway or activating degranulation of NKCs and/or eosinophils
c. Facilitate production of more antibodies (though action on B cells)
Steps for primary response would be similar (to secondary response for HUMORAL IMMUNITY), but would involve…
antigen presentation to Naïve B cells followed by clonal expansion in between steps 3 and 4
Adaptive Immunity – Humoral Immunity
Two categories of humoral immunity:
- Active Immunity
a. Natural
b. Artificial - Passive Immunity
a. Natural
b. Artificial
Adaptive Immunity – Humoral Immunity
- Active Immunity
body is exposed to the pathogen and produces its own antibodies via humoral immune response
Adaptive Immunity – Humoral Immunity
- Active Immunity
a. Natural
pathogen infects body through natural means (crosses barriers, evades innate immune system and triggers a normal humoral immune response that leads to the production of antibodies. Person becomes ill and then recovers.
Adaptive Immunity – Humoral Immunity
- Active Immunity
b. Artificial
Vaccination:
i. Vaccines mimic the pathogen. Can be composed of:
- Attenuated or killed pathogen
- Purified macromolecules
- DNA
All cause slow primary responses, which makes them harmless (mild symptoms at worst)
ii. Fake pathogen triggers creation of antibodies and memory cells (long-term immunity)
iii. Subsequent exposure to real pathogen (the memory cells) produces fast and more effective secondary response.
i. e. vaxxed person is later infected by the pathogen
Vaccination
containing dead or disabled pathogens or their products
existence of a secondary immune response is what allows vaccinations to be an effective protection from disease
Vaccines
contain an altered pathogen that no longer harms the host but that can be recog. as foreign by immune cells
Adaptive Immunity – Humoral Immunity
- Passive Immunity
the body acquires antibodies that were made by another individual or organism (often horses, sheep).
Adaptive Immunity – Humoral Immunity
- Passive Immunity
a. Natural
e.g. the antibodies that pass from mother to fetus across the placenta or through breast milk.
Adaptive Immunity – Humoral Immunity
- Passive Immunity
b. Artificial
injections that contain antibodies (antiserums) as opposed to attenuated pathogen.
- E.g.1: antivenin for snake bites
- E.g.2: convalescent serum for treatment of severe COVID-19 or ebola. Convalescent serum is produced by taking antibodies from a recovered person, and injecting them into someone who is ill to boost their immune response.
- E.g. 3: used for post-exposure injections for several conditions like rabies, tetanus, and Hepatitis B (if the person was exposed and had not been vaccinated).
